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“This suggests that a higher level of protein from BDNF gene expression may provide a buffer, or reserve, for the brain and protect it against the effects of the plaques and tangles that form in the brain as part of Alzheimer’s disease,” lead researcher Dr. Aron Buchman said in a statement.

Buchman and his colleagues followed 535 people with an average age of 81 until their death, for an average of six years. The study participants took annual tests of their thinking and memory skills, and after death, a neurologist examined their records to determine whether they had dementia, mild cognitive impairment, or no thinking and memory problems.

In people with the highest amount of Alzheimer's disease hallmarks in their brains, cognitive decline was about 40 percent slower for people with the highest amount of protein from BDNF gene expression compared to those with the lowest amount.

Thinking and memory skills declined about an average of 0.10 units per year on the tests. Higher levels of protein from BDNF gene expression reduced the effect of plaques and tangles in the brain on cognitive decline by 0.02 units per year.

This discovery could lead to new and more effective treatment for Alzheimer’s disease. There are no drug treatments that can cure the neurodegenerative condition, but medicines have been developed for Alzheimer's disease that can temporarily alleviate symptoms, or slow down their progression, in some people. The benefits of these drugs are small, according tothe Alzheimer’s Society.

The research does not prove a causal relationship between BDNF and a slower rate of cognitive decline, but Buchman told HealthDay it could encourage scientists to take a "whole different approach to aging." Instead of looking for ways to tackle plaques and tangles in the brain, which has been a futile effort, researchers could instead focus on increasing BDNF levels in the brain.

"That may be a way of treating and slowing the rate of mental decline even if we can't get rid of the Alzheimer's disease pathology in the brain," Buchman said.

Researchers said further work is needed to find a way to raise BDNF levels and to determine if activities which increase brain BDNF gene expression levels protect or slow the rate of cognitive decline in old age.